Apparatus for regulating the duration of a square-wave signal in an electronic injection control installation for diesel engines

ABSTRACT

An electronic apparatus for controlling the injection period of internal combustion engines having electromagnetic fuel injectors in accordance with a predetermined relation between injection period and engine speed. A pulse generator synchronized with engine rotation generates pulses corresponding to each successive injection period. Each pulse triggers a function generator for developing a reference voltage which is a real time analog of a predetermined curve of fuel quantity per injection (or injection period) versus time between injections. Each pulse simultaneously triggers a circuit for generating a rectangular delay signal of a variable duration which is inversely proportional to a selected engine speed. A memory circuit initiates the development of a regulating voltage in response to the termination of the rectangular delay signal. The magnitude of the regulating voltage rises from zero until it corresponds to the instantaneous value of the simultaneously developing analog reference voltage and then follows the reference voltage until initiation of the succeeding pulse from the pulse generator. A fuel injection signal generator initiates a rectangular fuel injection signal in response to the succeeding pulse from the pulse generator, the duration of the injection signal being a direct function of the instantaneous value of the regulating voltage at the moment of initiation of the injection signal.

United States Patent Advenier n] 3,800,749 [451 Apr. 2, 1974 APPARATUS FOR REGULATING THE DURATION OF A SQUARE-WAVE SIGNAL IN AN ELECTRONIC INJECTION CONTROL INSTALLATION FOR DIESEL ENGINES [75] Inventor: Pierre M. Advenier, Paris, France [73] Assignee: Sofredi, Clichy, France [22] Filed: July 26, 1971 21 Appl. No.: 166,150

[30] Foreign Application Priority Data Aug. 14, 1970 France 70.29983 [52] US. Cl. 123/32 EA, 123/139 E [51] Int. Cl. F02b 3/00, F02m 39/00 [58] Field of Search 123/32 EA [5 6] References Cited UNITED STATES PATENTS 3,660,689 5/1972 Oishi 123/32 EA 3,651,792 3 1972 Monpetit Q3/3211 3,575,146 4/1971 Creighton.... 123/32 EA 3,710,766 1/1973 Beishir 123/32 EA 3,653,365 4/1972 Monpetit 123/32 3,645,240 2/1972 Monpetit 123/32 Primary Examiner-Laurence M. Goodridge Assistant ExaminerRonald B. Cox

Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT An electronic apparatus for controlling the injection period of internal combustion engines having electromagnetic fuel injectors in accordance with a predetermined relation between injection period and engine speed. A pulse generator synchronized with engine rotation generates pulses corresponding to each successive injection period. Each pulse triggers a function generator for developing a reference voltage which is a real time analog of a predetermined curve of fuel quantity per injection (or injection period) versus time between injections. Each pulse simultaneously triggers a circuit for generating a rectangular delay signal of a variable duration which is inversely proportional to a selected engine speed. A memory circuit initiates the development of a regulating voltage in response to the termination of the rectangular delay signal. The magnitude of the regulating voltage rises from zero until it corresponds to the instantaneous value of the simultaneously developing analog reference voltage and then follows the reference voltage until initiation of the succeeding pulse from the pulse generator. A fuel injection signal generator initiates a rectangular fuel injection signal in response to the succeeding pulse from the pulse generator, the duration of the injection signal being a direct function of the instantaneous value of the regulating voltage at the moment of initiation of the injection signal.

14 Claims, 4 Drawing Figures CSR PATENTEDAPR 2 1974 SHEET 3 0F 3 MAAEA/Toe aw URN/5V5 APPARATUS FOR REGULATING THE DURATION OF A SQUARE-WAVE SIGNAL IN AN ELECTRONIC INJECTION CONTROL INSTALLATION FOR DIESEL ENGINES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to apparatus for regulating the duration of a square-wave electric signal for controlling the amount of fuel injected in an electronic injection control system for Diesel engines.

2. Description of the Prior Art French Patent No. 1,581,459 in the name of the assignee of this application, describes an electronic injection control method and apparatus for adjusting the quantity of fuel injected per cycle as a linear function of the duration of an electric signal applied to an injector or transducer.

In the apparatus of that patent, the duration of constant injection is regulated by maintaining constant the duration of the electric signal constant for all speeds of rotation below a predetermined value and by gradually reducing the signal duration as the speed of rotation increases above that value until the injected quantity becomes zero. In the aforesaid patent a pulse corresponding to each injection triggers a rectangular reference signal, the duration of which is adjustable as a function of the speed of rotation displayed by an engine speed selector. The end of the said reference signal initiates a variation of a regulating voltage, the said regulating voltage then determining the duration of a rectangular injection control signal triggered by the pulse succeeding the one which initiated said rectangular reference signal.

The foregoing apparatus makes it possible to maintain the duration of the injections, and hence the injected quantity, constant independently of the speed of rotation of the engine until the speed regulation becomes effective at the speed of rotation displayed by the selector. Now, particularly with Diesel engines, it is preferable not to inject a constant quantity of fuel, but to vary it as a function of the speed of rotation of the engine to reflect on the one hand the amount of air Charged in the cylinders of the engine as a function of the speed of rotation (i.e., the volumetric efficiency, and on the other hand the torque desired from the engine to match the load to which it is subjected. The amount of fuel injected and hence the torque developed by the engine, as a function of the speed of rotation, is generally expressed by a convex curve whose maximum corresponds to the maximum torque of the engine, and whose extremities determine the quantities to be injected (as well as the torque developed) at idle and at maximum speed respectively. Such a curve may be approximated to the desired degree of precision by means of a series of straight line segments, the simplest shape obviously being a a straight rising line and a straight descending line with the corresponding apex at the maximum quantity to be injected. In order to facilitate starting, it may furthermore be arranged that the injected quantity is very greatly increased in the speed range from zero up to a low speed of rotation below the normal idling speed of the engine.

SUMMARY OF THE INVENTION The present invention has for its object to provide an injection control apparatus which varies the injected quantity as a function of the speed of rotation in accordance with a curve as described above.

The apparatus for regulating the duration of a square-wave electric signal in an injection control installation of the present invention comprises a pulse generator slaved to the rotation of the engine for generating a short pulse to initiate each injection period, a function generator for developing a reference voltage which is a real time analog of a predetermined curve of fuel quantity per injection versus time between injections, means for generating a rectangular delay signal of adjustable duration in response to the pulses of the pulse generator a memory circuit for developing a reg ulating voltage upon the termination of each rectangular delay signal, the value of said regulating voltage rising from zero until it corresponds to the instantaneous value of the simultaneously developing analog reference voltage and then following the reference voltage until stopped by the pulse which follows that which initiated the preceding rectangular delay signal, and a fuel injection signal generator for producing a rectangular fuel injection signal in response to said following pulse, the duration of the injectionsignal being a function of the instantaneous value of the regulating voltage when its development was stopped by said following pulse. A preferred embodiment of the function generator of the invention comprises as many monostable multivibrators and current generators as there are straight line segments of the analog curve. Each of said monostable multivibrators is switched simultaneously into the astable state by each pulse of the pulse generator for different preset periods, at the end of which the associated current generators at are rendered conductive. The amount'and direction of the current produced by each generator is preselected, and the outputs of all generatorsare combined as the generators become conductive in turn, to develop successive segments of the analog reference voltage. Upon the next pulse from the pulse generator, the reference voltage is reduced to zero by means of a switching element.

The memory circuit for developing a regulating voltage is connected by switching elements to the pulse generator and to the function generator, as well as to the means for generating the rectangular delay signal, so that the regulating voltage rises with an adjustable slope after the triggering the memory circuit at the end of the rectangular delay signal to join the reference voltage and then to follow it until its development is stopped by the pulse which follows that which initiated the rectangular delay signal. The memory is designed to store the instantaneous value of the stopped regulating voltage determined by the said for the duration of the injection determined by the said triggered by the pulse which caused the stoppage, said value determining the duration of said injection In a specific embodiment of the function generator, the initial value of the reference voltage is produced by a voltage divider connected across a voltage supply to yield a constant voltage at the terminal of a capacitive storage element during a first time period determined by the astable period of a first monostable multivibrator. The first monostable multivibrator triggers a first current generator at the, end of the first time period to supply a current to charge the capacitive element, causing the reference voltage at the element to rise with a first predetermined slope. At the end of a second time period, a second monostable multivibrator triggers a second current generator to supply a current of opposite direction of the first current to discharge the capacitor, causing the reference voltage at the capacitive element to fall with a second predetermined slope. Finally a third monostable multivibrator triggers a third current generator at the end of a third time period to supply a current of the same direction as the first current causing the reference voltage at the element to again rise with a third predetermined slope, the reference voltage thereafter becoming stabilised at a constant value. A first switching element is provided which discharges the capacitor in response to each pulse from the pulse generator.

The means for generating the rectangular delay signal preferably comprises a fourth monostable multivibrator which triggers a fourth current generator at the end of a delay period that is an inverse function of desired engine speed to supply a current which causes the previously described regulating voltage to rise in accordance with a predetermined slope across the terminals of the memory circuit. A second switching element in the form of a threshold device sensitive to the voltage across the terminals of the memory and to the reference voltage becomes conductive to divert the current from the fourth current generator when the memory reaches a voltage corresponding to the reference voltage. A third switching element is also provided, which is actuated by the second switching element when the latter is conductive to establish a connection between the function generator and the memory which causes the regulating voltage to follow the development of the reference voltage.

A fifth monostable multivibrator cooperating with an amplifier initiates a rectangular injection control signal in response to each pulse from the pulse generator. Through a connection being provided between the memory and the fifth monostable multivibrator, the value of the regulating voltage at the instant of the corresponding pulses from the pulse generator determines the duration of the injection control signal. Finally, fourth switching element is connected to the amplifier and actuated by the latter at the end of each injection control signal to erase the information in the memory.

Each of the monostable multivibrators preferably comprises a programmable unijunction transistor connected in parallel with a capacitor and the collectoremitter circuit of an input transistor. The junction point between the collector of said input transistor, one of the terminals of the capacitor, and the anode of the programmable unijunction transistor is connected to the supply voltage through resistors, at least one of which is variable. The emitter of said input transistor, the other terminal of the capacitor, and the cathode of the programmable unijunction transistor are connected to earth, the cathode optionally through a resistor. The control electrode of the said programmable unijunction transistor is fixed at a certain potential by a voltage divider or the memory. The current generators comprise at least one transistor whose base is directly or unidirectly connected either to the control electrode or to the cathode of the programmable unijunction transistor, and the base of the input transistor of each monostable multivibrator is connected to the pulse genera- I01.

The memory circuit preferably comprises a capacitor connected to earth at one of its terminals, with a diode and a resistor connected in parallel to the other terminal of the capacitor. The memory transmits a regulating voltage taken from the terminals of the capacitor to the injection signal generator through an impedance matching device in the form of two transistors of the common-supercollector type.

The second switching element preferably comprises a programmable unijunction transistor whose anode is connected to the input of the memory circuit, whose cathode is connected to earth through two resistors and whose control electrode is connected to the output of the function generator through an impedance matching device comprising two transistors of the commonsupercollector type. The second switching element actuates the third switching element which comprises two transistors through a connection between the junction point of the two resistors and the base of the programmable unijunction transistor, the third switching element acting on the transistor in the impedance matching device that is connected as an emitter-follower, so that the reference voltage appears at the emitter of that transistor when the programmable unijunction transistor in the second switching element is conductive.

The fourth switching element preferably comprises a transistor connected with its collector-emitter circuit in parallel with the capacitor of the memory. The base of said transistor is connected through a capacitor and a resistor to the collector of a transistor in a threetransistor amplifier which is non-conductive in the absence of an injection signal, so that a positive pulse transmitted at the end of each injection to the base of the transistor renders it conductive, hence discharging the capacitor.

A safety device comprising a time delay switch actuated by the engine starter switch preferably is disposed at the input of the third monostable multivibrator, so that the third monostable multivibrator and its associated current generator can become operative only at the instant of starting the engine.

BRIEF DESCRIPTION OF THE DRAWINGS By way of example and for a readier understanding of the following description, there are shown in the accompanying drawings:

FIG. 1 is a block diagram of the whole injection installation on a direct injection internal combustion englne,

FIG. 2 is a graph of the quantity of fuel to be injected per cycle as a function of the speed of engine rotation,

FIG. 3 is a schematic diagram of an electronic injection control system according to the invention, and

FIG. 4 is a waveform diagram showing the development of the voltages at various points of the circuit as a function of time.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, an internal combustion engine comprises an intake manifold 87 and electromagnetically controlled injectors 20 disposed in the cylinder head of the engine for direct injection of fuel. The injectors are fed with fuel under constant pressure through a fuel line 93 connected through a filter 89 to a supply pump 92, which draws from a supply tank 99,

the pressure of the fuel being maintained constant by means of pressure regulator 90. In addition, a hydraulic pressure accumulator 88 is provided to reduce the pressure pulsations at the output of pump 92. The injections are triggered by a pulse generator I as a function of the speed of rotation of engine 85, the pulses of pulse generator I being sent to monostable multivibrators MM.I, MM.2, MM.3 associated with current generators GL1, GL2, GL3, respectively. In addition, the pulses are sent to a delay as generating means CSR and to first switch element CO.3. The termination of the rectangular delay signal generated by means CSR actuates a current generator GC, while the current generators GL1, GL2, GL3 actuated by the monostable multivibrators MM.1, MM.2 and MM.3, respectively, feed a device VR for developing an analog reference voltage, the device VR being in addition subjected to the action of the first switch element CO.3.

Under the combined action of current generator GC and device VR through second and third switch elements CO1 and CO2, a regulating voltage is developed in a memory circuit M to determine the duration of the injections by acting on an injection control device CDL The injection control signals are thereafter applied to the injectors 20 through an amplifier A and a distributor D which distributes them among the injectors in accordance with the desired firing order of the injections. At the end of each injection, the information stored in memory M is erased by a fourth switch element CO4.

FIG. 2 is a graph of the quantity to be injected per cycle, and hence of the duration of the injections, as a function of the speed of rotation of the engine. This curve comprises a first very accentuated maximum intended to give an over-injection at starting. The convex curve which joins this over-injection below the idlerunning speed corresponds to the quantity to be injected as a function of the real requirements of the engine, which are determined on the test benches by adjusting the quantity point-by-point. and increasing the speed of rotation under full load. The form of the curve is, as already stated, essentially a function of the volumetric efficiency of the engine, which is in turn a function of the speed of rotation and generally has a maximum at the speed of rotation of maximum torque, this maximum being due inter alia to the effects of resonance in the intake and exhaust manifolds. It is to be noted that this curve may in addition be adapted to the conditions of use of the engine in order to obtain a torque curve of the engine which rises as required.

This curve may be approximated by a series of straight line segments, and the precision of. the approach depends only upon the number of segments employed. In the described case, the curve is approximated by a rising straight line and a descending straight line having their points of intersection with the curve at idle speed, at the maximum torque speed, and at the maximum speed of rotation of the engine. The inclined lines Q1, 0.2, Q3, 0.4 indicate the drop in fuel injected per cycle above various speeds of rotation as predetermined by an adjustable speed selector. It will thus be seen that as long as the speed of rotation is below a predetermined value, for example determined by the intersection of the rising straight line segment with line 0.4, the injected quantity follows the rising line, but above that predetermined speed the injected quantity decreases rapidly along line Q.4.to become zero if the engine tends for any reason to turn at a speed higher than the selected speed.

The apparatus of the present invention is designed to control the period of each injection, and thereby the amount of fuel injected, by means of an analog voltage signal that corresponds to an experimentally derived curve such as that shown in FIG. 2.

As discussed above, the abscissa of the graph of FIG. 2 is measured in terms of engine speed, that is, revolutions per unit time. The abscissa of a real-time analog of this curve, on the other hand, of necessity must be measured in units of time, or the inverse of the base of the curve in FIG. 2. Thus, the analog regulating voltage developed by the apparatus of the invention must be equivalent to the curve of FIG. 2 developed backwards, that is, from right to left instead of from left to right.

The preferred means for obtaining this analog regulating voltage are described in detail with reference to FIGS. 3 and 4.

In the circuit of FIG. 3, the monostable multivibrator MM.1 and the current generator GL1 develop a straight line increasing voltage, corresponding to the right hand segment of FIG. 2, and the monostable multivibrator MM.2 and current generator GL2 develop a straight line decreasing voltage, corresponding to the segment of FIG. 2 between idle and engine speed at maximum fuel injection. The monostable multivibrator MM.3 and the current generator GL3 are designed to give the over-injection at starting by developing a rapidly rising voltage to a high constant value corresponding to the initial portion of FIG. 2. The monostable multivibrators MlVLl, MM.2, MM.3 are substantially identical and comprise the input transistors T.1, T.6 and T.10 are respectively connected at their bases to the pulse generator I through resistors R.l, R.l6 and R.26. Connected in parallel with the collector-emitter circuit of said transistors are capacitors G1, G3 and CA, as well as programmable unijunction transistors 17.2, T.7 and T.1'1. In the case of monstable multivibrator MM.2, the cathode of programmable unijunction transistor T.7 is not directly connected to earth as in the case of the other monostable multivibrators MM.1 and MM.3, but through a resistor R.l9. The anodes of the programmable unijunction transistors T.2, T.7, T.1 1 are connected to a supply voltage VA through the resistors R2, R3; R17, R.l8 and R.27, R.28 respectively, the resistors R.3, R.l8, and R.28 being adjustable to be able to vary the astable period of each of said monostable multivibrators. The voltages at the control electrode of the programmable unijunction transistors 'l':.2, T.7, T.l1 are established by voltage dividers comprising resistors R.4, R5, R6; R20, R21 and R.29, R.30, R31, respectively.

The device VR for developing the analog reference voltage consists simply of a capacitor C2, operating in conjunction with a circuit element VR.l which will subsequently be described, and which is charged in response to each pulse from the pulse generator initially to a constant voltage by the device V0, followed by successive increasing and decreasing voltages in response to successive actuation of the current generator GL1, the current generator CL2 and the current generator CL3 from the instant when they become operative under the respective control of monostable multivibrators MM.1, MM.2 and MM.3.

As indicated in curve C of FIG. 4, the reference voltage commences with a horizontal portion of duration T.l. This horizontal portion is determined by device V in FIG. 3, which is essentially a voltage divider comprising a resistor R.10, a potentiometric voltage divider R11 and a resistor R.l2 connected in series between the supply voltage and earth. The slider of potentiometric voltage divider R.1l is connected to one terminal of capacitor C.2 through a diode D.2, said one terminal being connected in addition to the collector of transistor T.3. The emitter of transistor T.3 is connected to the supply voltage through resistors R8 and R.9, the latter being variable, and the base is connected to the junction point of resistor R5 and diode D.1 in monostable multivibrator MM.1.

Current generator GL2, is also connected to the capacitor C.2, comprises a transistor T.8, connected at its base to the cathode of a programmable unijunction transistor T.7 through a resistor R22, and a transistor T.9, connected at its base to the emitter of a transistor T.8 and in addition to earth through diode D3 and resistor R.23. The collector of transistor T.8 is connected to the supply voltage. The emitter of transistor T.9 is also connected to earth through resistors R.24 and variable resistor R.25, while the collector of transistor T.9 is connected to capacitor C.2 through diode D4.

Current generator GL3 comprises a transistor T.l2, whose base is connected to the junction point of resistor R30 and diode D7 in monostable multivibrator MM.3. The emitter of transistor T.l2 is connected to the supply voltage through resistors R.32, R33, the latter being variable, while the collector of transistor T.l2 is also connected to capacitor C.2 through diode D6. A first switch element CO.3, comprising a transistor T4 connected at its collector to the capacitor C.2, with its emitter earthed and with its base connected to the pulse generator through the resistor R.7, discharges capacitor C.2 in response to each pulse from pulse generator l. The analog reference voltage developed across the terminals of the capacitor C2 is then obtained in the following manner:

Each time generator pulse emitter I sends a pulse to the bases of transistors T.l, T.4, T.6 and T.l0, the transistors become conductive, and capacitors C.1, C.2, C.3 and C4 are completely discharged. Consequently, the programmable unijunction transistors T.2, T.7 and T.ll become non-conductive due to the lack of current if they were previously conductive. As soon as the pulse disappears, transistors T.l, T.4, T.6 and T.l0 become non-conductive. Hence, capacitors C.l, C.3 and CA become charged through resistors R2, R3; R.l7, R.18 and R.27, R.28, respectively, the time constant of these circuits depending upon the resistance of their respective resistors and upon the capacitance of capacitors C.l, C.3 and CA.

Capacitor C.2 is very rapidly charged initially to a constant voltage determined by the voltage divider consisting of the resistors R10, R11 and R.l2. The resistance of RB in monostable multivibrator MM.1 is so adjusted that the voltage across the terminals of capacitor C.l reaches a certain value in relation to the voltage applied to the control electrode of the programmable unijunction transistor T.2 at the end ofa time T; from the occurrence of the preceding pulse from generator I, where T, is equal to the time between injections at maximum engine speed. At this instant, programmable unijunction transistor T.2 suddenly becomes conductive due to the avalanche effect, and the potential of the control electrode becomes equal to that of the anode. Consequently, the base voltage of transistor T.3 is reduced to the point that the transistor becomes conductive. Since transistor T.3 is connected as a current generator, capacitor C.2 is charged with a constant current ii.

In FIG. 4, the voltage across the terminals of capacitor C.2 is illustrated by curve C. It will be seen that the voltage remains constant during period T, and thereafter rises with a certain slope which depends upon the value of the charging current i1. The slope is adjustable by variable resistor R9.

Monostable multivibrator MM.2 in its turn is adjusted so that the end ofa time T equal to the time between injections at the speed corresponding to maximum fuel injection programmable unijunction transistor T.7 and transistor T.6 of monostable multivibrator MM.2 become conductive. Since resistor R19 is connected between the cathode of programmable unijunction transistor T.7 and earth, a voltage is established across its terminals which is applied to the base of transistor T.8 in current generator GL2. Transistor T.8 then becomes conductive, and transistor T.9 consequently also becomes conductive. A current i2 then passes through resistor T.9 from the discharge of capacitor C.2 through diode D4. By appropriate adjustment of the variable resistor R.25, the value of the current i2 is higher than that of the current i1. Consequently, the voltage across the tenninals of capacitor C.2 decreases in a straight line after time T235 indicated in Curve C of FIG. 4.

It is to be noted here that capacitor C.2 normally cannot be discharged by current generator G2 to a voltage lower than that determined by the voltage divider in device VO because whenever the voltage across the terminals of capacitor C.2 tends to become lower, diode D2 is no longer biassed and supplies a current which is equal to the difference between the currents i2 and i1. However, since in some cases it is preferable to be able to reduce the voltage across the terminals of capacitor C.2 to a value lower than that defined by the voltage divider consisting of resistors R10, R11 and R12, it is possible to lower the voltage determined by device VO during the time when generator Gl.2 is in operation. To this end, there is a connection between the cathode of programmable unijunction transistor T.7 and the base of transistor T5 through resistor R.l5. The collector of transistor T5 is connected to the slider of potentiometric voltage divider R.11 through a variable resistor RM and a fixed resistor R.l3, while its emitter is connected to earth. Transistor T.5 is therfore conductive at the same time as transistor T.8 and T.9, and it lowers the voltage applied to the diode D2, since the voltage divider which defines this voltage no longer comprises only the resistors R10, R12 and the potentiometric voltage divider R.1l, but the resistors R.13 and R14 are added in parallel with the resistor R.12 and a part of the potentiometric voltage divider Roll.

At the end of a time T equal to the time betwen injections at minimum idle speed monostable multivibrator MM.3 is adjusted so that programmable unijunction transistor T.ll suddenly becomes conductive in the manner described in the foregoing. The potential of its control electrode is then reduced to a very low value, thus lowering the potential of its base, and transistor T.l2 consequently becomes conductive. Resistors R,32, R33 are here so designed that transistor T.l2

supplies a current is which is substantially higher than the sum of the currents i1 and i2. The voltage across the terminals of capacitor C2 then rises very rapidly and reaches a value which depends upon the adjustment of current generator GI.3

It is obvious that the complete development of the reference voltage which has just been described takes place only if no pulse meanwhile arrives from pulse generator I. This is the case only at starting, and it is precisely at this condition that a boost injection of fuel is required. To make certain that the injection boost can take place only at starting, there may be provided a starting safety device SD which is disposed between pulse generator I and the connection to transistor T.l of monostable multivibrator MM.3. This safety device SD may be at a time delay relay connected, for example, to the contact of the starter. Thus injection boost can take place only when the starter contact is closed to start the engine. By providing a time-delay relay, the injection boost may continue for a set time after starting the engine, after which it is cut off. Consequently, injection boost cannot take place accidentally when the speed of rotation of the engine under load momentarily falls below the idling speed of rotation.

As already stated in the foregoing, each pulse emitted by pulse generator I completely discharges capacitors C1, C2, C3 and C.4 and thus brings monostable multivibrators MM.1, MM.2, MM.3 and device VR to a starting condition. As a result, the evolution of the analog voltage across the terminals of capacitor C.2 is interrupted each time a pulse appears at the bases of transistors T.l, T4, T6 and T.l0, and the analog reference voltage commences a fresh cycle. Therefore, depending on the time elapsing between two successive pulses, the evolution of the reference voltage across the terminals of the capacitor C2 is stopped at different points of the curve. FIG. 4, illustrates three examples of the evolution of the reference voltage, depending upon whether the pulse 1 is followed by a pulse 2, 2, or 2", which correspond to different engine operating conditions to be described after discussion of the remaining circuit elements of FIG. 3.

The analog reference voltage in turn determines the quantity to be injected under full load by acting on the following circuit elements. The analog reference voltage is applied to device VR, which comprises transistors T.22, T.23 arranged with a common supercollector, the reference voltage being applied to the base of transistor T23 through a resistor R.55. The collector of transistor T23 is connected to the base of transistor T.22, the emitter of transistor T.22 is connected to the supply voltage, and the collector of transistor T.22 and the emitter of transistor T23 is connected to earth through a common resistor R.54.

The arrangement of transistors T.22, T.23, serves essentially for impedance matching, and the reference voltage will be present at the common connection of the collector of transistor T.22 and the emitter of transistor T.23. This voltage is applied to the base of a transistor T.2l through a resistor R.53, the collector of transistor T.2l being connected to the supply voltage, while its emitter is connected across the terminals of capacitor C6 forming part of the memory M.

Since transistor T21 is connected as an emitterfollower, the reference voltage than also appears at its emitter and in addition is connected to the base of a transistor T.25 in an injection control device CDI through a resistor R57. It should be noted, however, that the transistor T21 is conductive only if a third switch element CO.2 permits it, said switch CO2 including transistors T.l9 and T20. The latter transistor is connected by its collector to the base of transistor T21, transistor by its emitter to earth, and by its base to che collector of a transistor T.l9 through a resistor R52. The collector of transistor T.l9 is in addition connected to the supply voltage through resistor R5], its emitter is connected to earth, and its base is connected to a second switch element CO1; consequently, the state of switch CO2 depends upon the state of switch C01. The state of switch CO1 depends, in turn, upon the information in the memory M, this information being determined on the one hand by a delay signal control device CSR and a current generator GC, and on the other hand by the reference voltage appearing at the output of device VR.

The rectangular delay signal control device CSR consists of a monostable multivibrator analogous to those already described. It includes a transistor T.l4 which receives at its base each pulse from pulse generator I through a resistor R34, transistor T.l4 being connected at its emitter to earth and at its collector to the supply voltage through resistors R and R36, R37, the latter two being adjustable. A capacitor C5 is connected in parallel with the collector-emitter circuit of transistor T.l4, and a programmable unijunction transistor T.l5 is connected in series with resistors R.38, R39. The control electrode of programmable unijunction transistor T.l5 is fixed at a certain potential by a voltage divider comprising resistors R40, R41 connected between the supply voltage and earth.

The current generator GC includes a transistor T.l6 with its collector-emitter base connected between earth and the supply voltage through resistor R.43, a diode D8 and resistor R.42. The base of transistor T.l6 is connected to the junction point of resistors R.38 and R39. A transistor T.l7 also forms part of current generator GC and is connected at its base to the junction point of the diode D8 and resistor R.43, at its collector to capacitor C.6 through diode D9 in parallel with resistor R46 and at its emitter to the supply voltage through variable resistor R45 and resistor R.44. Capacitor C6 and diode D9, together with resistor R.46, constitute memory M.

The second switch CO1 include a programmable unijunction transistor T.l8 connected at its anode to the collector of transistor T.l7 and at its cathode to earth through resistors R47 and R48, while its control electrode is connected to device VRl through a resistor R50 and to earth through a resistor R.49. Furthermore, a connection is provided between the base-of transistor T.l9 and the junction point of resistors R47 and R.48.

The injection control device CDI is essentially a monostable multivibrator of the type already described, comprising an input transistor T28 connected at its base to pulse generator I through a resistor R.64. The emitter of transistor T28 is connected to earth, while its collector is connected to the anode of programmable unijunction transistor T.27. The anode of T27 is also connected to the supply voltage through a resistor R61 and a variable resistor R.62, while its cathode is connected to earth through a resistor R.63. A capacitor C7 is in parallel with the collector-emitter circuit of transistor T.28.

The voltage applied to the control electrode of programmable unijunction transistor T.27 is determined by the information in the memory M through the connection from the junction point of capacitor G6 with the cathode of diode D9 to base of the transistor T.25 through resistor R57.

'1 he lntnfilsltim 1.25, 1.24 serve for impedance matching through the common supercollector arrangement employed here. For this purpose. the collector of transistor T is connected to the base of transistor T.24, and also to the emitter of the latter transistor through a resistor R56, the emitter of transistor T24 being connected in addition to the supply voltage. There is furthermore provided a connection between the emitter of transistor T.25 and the collector of transistor T.24. This connecting point is in addition connected to earth through a potentiometric voltage divider R.58. The slider of R58 is connected to the control electrode of programmable unijunction transistor T17 through a resistor R.59. The control electrode of T.27 is in addition connected to earth through a resis tor R.60.

The injection control signal taken from the cathode of programmable unijunction transistor T.27 is applied to an amplifier A, which includes transistors T.26, T29 and T.30. The base of transistor T19 is connected to the cathode of programmable unijunction transistor T27, while its emitter is earthed. The collector of transistor T.29 is connected on the one hand to the supply voltage through a resistor R65 and on the other hand to the base of transistor T through a resistor R66. The emitter of transistor T.30 is also connected to earth, and its collector is connected to the supply voltage through resistors R.67 and R.68. The emitter of transistor T.26 is connected to the supply voltage, while its collector is connected to earth through a resistor R.69. In addition, the base of transistor T.26 is connected to the junction point of resistors R.67 and R68.

An injection control signal is then taken from the collector of transistor T.26 and transmitted to distributor D (see HO. 1). ln addition, there is a connection between the collector of transistor T30 and a fourth switch element CO4 comprising a transistor T.l3 connected at its emitter to earth, at its collector to the junction point between diode D.9 and capacitor C6, and at its base both to the collector of transistor T.30, through a capacitor C8 and a resistor R70 and also to earth through a resistor R.7l. The system operates as follows:

Each pulse produced by pulse generator I is applied to the bases of transistors T.l, T.4, T.6, T.l0, T.l4 and T.28, which then become conductive for the duration of the pulse. As a result capacitors C.l, C.2, C.3, C.4, C5 and C7, respectively connected in parallel to these transistors, are discharged, thereby defining an initial starting state for the whole system. Upon termination of each pulse, the monostable multivibrators MM.1, MM.2, MM.3, CPR and CDI remain in their astable state for different periods determined in each case by the voltage applied to the control electrode of the respective programmable unijunction transistors T.5, T.7, TI 1, T.l5 and T.27 in these monostable multivibrators and by the circuit constants of each monostable multivibrator.

As already described, a reference voltage is thus developed at the output of the device VR, which will be employed to determine the duration of the injections. With regard to device CSR for generating the rectangular delay signal, it should be noted that because programmable unijunction transistor T.lS is not conductive during the charging of capacitor C5, the voltage applied to the base oftransistor T.l6 in current generator (3c is zero, and hence it is not conductive. Consequently, full supply voltage is applied directly to the base of transistor T.l7, which is then also rendered nonconductive. Therefore, during the charging of capacitor C.5, transistor T.l7 is non-conductive and cannot charge capacitor C6 in memory M. The charging duration of capacitor C5 depends upon the its capacitance and the resistances of resistors R.35, R.36 and R37. In the embodiment illustrated, variable resistor R.36 permits an initial adjustment, while variable resistor R.37 is connected to the speed selector of the engine not shown. Hence, by varying resistor R.37, it is possible to vary the engine speed.

As mentioned above during the charging period of capacitor C5, transistor T.l7 does not conduct the voltage across the terminals of capacitor C.6 remains zero, and hence the voltage applied to the anode of programmable unijunction transistor T.l8 in second switch element CO.1 also remains zero. The latter therefore cannot be triggered even when a voltage following the analog reference voltage applied to its control electrode. As soon as the charging voltage of capacitor C.5 reaches a certain voltage in relation to the value applied to the control electrode programmable unijunction transistor T.l5, the latter is triggered by avalanche effect, and a predetermined voltage is set up across the terminals of reistor R.39 this voltage being applied to base of the transistor T.l6. The latter then becomes conductive, and also transistor T17.

Since transistor T17 is connected as a current generator, it charges capacitor C6 with a constant current determined by resistors R44 and R45. Consequently, the voltage applied to the anode of programmable unijunction transistor T.l8 rises with the charge of capacitor C.6. When this voltage applied to the anode of transistor T.l8 reaches a certain value in relation to the voltage applied to its control electrode, transistor T.l8 is also triggered by avalanche effect. As a result, the charge current of capacitor C6 determined by the current generator GC is shunted through programmable and unijunction transistor T.l8, and the voltage across the terminals of capacitor C6 no longer depends upon this current.

From the instant when programmable unijunction transistor T.l8 becomes conductive, a voltage is established across the terminals of resistor R.48 and is applied to the base of transistor T.l9, thus rendering it conductive. Consequently, the voltage previously applied to base of the transistor T20 disappears, and the latter becomes non-conductive. This allows the analog reference voltage to be applied through resistor R53 to the base of transistor T21, and since T.2l is connected as an emitter-follower, an analogous voltage appears at its emitter. Consequently, the reference voltage, to a close approximation, is applied to memory M from the instant when programmable unijunction transistor T.l8 becomes conductive. The voltage on capacitor C6 of memory M therefore exactly follows the development of the analog reference voltage as it appears on capacitor C2 of device VR, resistor R.46 permitting the charge on capacitor C.6 to decrease whenever the reference voltage falls.

Referring to FIG. 4, it will therefore be seen that pulse 1 on line a triggers a rectangular delay signal of duration T (line b) said delay signal being produced by device CSR and applied to current generator GC, thus rendering it inoperative for the period. To the duration of the rectangular delay signal is externally adjustable, for example by means of the engine speed selector.

At the same time, pulse 1 triggers a device VR. which applies the analog reference voltage of curve C through switches CO.1 and CO2 to memory M to provide it with information concerning the duration of the next injection.

As described above these switches are so connected that the memory receives information only from the instant when the delay signal of duration T is terminated. From this instant a regulating voltage is developed across the terminals of capacitor C.6 in curve d of memory M, as indicated in FIG. 4, this voltage being the information concerning the injection to be triggered by pulse 2 of line a in FIG. 4. As already stated, current generator GC initially charges memory M in a straight line starting from the instant when the rectangular delay signal ends, joining the reference voltage and following it until the appearance of succeeding pulse 2, as shown on line a of FIG. 4. At this instant, the reference voltage is reduced to zero, but the instantaneous value of regulating voltage VM in memory M remains stored until the end of the injection triggered by pulse 2.

As earlier described, regulating voltage VM developed across capacitor C.6 is applied to injection control device CD1 and determines the duration Ti of the injection signal. At the end of each injection, transistor T.30 is rendered non-conductive and consequently a positive voltage is established at its collector. This positive voltage is transmitted in the form of a pulse to the base of transistor T.l3 in the fourth switch CO.4, which becomes conductive for the duration of the pulse, thereby discharging capacitor C.6 of memory and erasing the stored information regarding the duration of the preceding injection.

Consequently, the duration Ti of each injection is determined by the value of the voltage VM at the instant of the occurrence of the injection control pulse which follows that which initiated the development of the corresponding reference voltage by device VR and the formation of the corresponding delay signal T by device CSR.

If the speed of rotation increases to the speed predetermined by the speed selector, the pulses approach one another as indicated by the pulse 2', and the development of regulating voltage VM is stopped before reaching the reference voltage. Consequently, the regulating voltage is low and the duration of the subsequent injection is short, as indicated by Ti on line e. If engine speed increases further for some reason, the injection periods would become zero as soon as the time between pulses l and 2' becomes equal to or shorter than the duration of the delay signal. On the other hand, if the engine turns very slowly, as at the time of starting, for example, a following pulse 2' arrives at the end of a time which is sufficiently long to enable the reference voltage, and hence the regulating voltage, to reach a very high value for boosted injection. Consequently, the injection period Ti, and hence the injected quantity, is considerably increased to facilitate starting.

It will therefore be seen that it is possible by means of the system of the invention to regulate the amount of fuel injected over the whole speed range of the engine, with the quantities injected under full load being corrected for the volumetric efficiency of the engine and the quantities injected under other load conditions being determined by the engine speed selected by the operator.

I claim:

1. An electronic apparatus for controlling the injection periods of diesel engines having electromagnetic fuel injectors in accordance with a predetermined relation between injection period and engine speed under full load, the apparatus comprising:

a pulse generator synchronized with engine rotation for providing a short triggering pulse corresponding to each successive injection period;

a function generator connected to the pulse generator for developing an analog reference voltage in response to a first triggering pulse from the pulse generator, the value of the analog reference voltage varying as a function of time after the first triggering pulse so as to reproduce a predetermined curve of fuel quantity per injection versus time between injections under full load conditions at all engine operating speeds, the development of the analog reference voltage being terminated in response to a second triggering pulse next succeeding the first triggering pulse from the pulse generator;

means for selecting a desired engine speed;

a delay signal generator connected to the pulse generator and the speed selecting means for initiating a rectangular delay signal of variable duration in response to the first triggering pulse, the duration of the signal being controlled by the speed selection means as an inverse function of the selected speed;

means connected to the pulse generator, the delay signal generator and the function generator for developing a regulating voltage waveform that is initiated in response to the termination of the rectangular delay signal, that rises from zero at a predetermined rate until it corresponds in value to the analog reference signal, and that follows the value of the analog reference signal until receipt of the second triggering pulse next succeeding the first pulse from the pulse generator; and

a fuel injection signal generator connected to the pulse generator and to the means for developing the regulating voltage waveform for initiating in response to the second triggering pulse a rectangular fuel injection signal for actuating one of the fuel injectors, the duration of the fuel injection signal being determined by the value of the regulating voltage at the instant of the second triggering pulse, the second triggering pulse then serving as a first triggering pulse for initiating development of the analog reference voltage by the function generator for controlling the duration of the next succeeding fuel injection signal, whereby the amount of fuel injected during each fuel injection signal will increase to full load values if engine speed falls below the set speed and will decrease to zero if engine speed increases above the set speed.

2. The injection control apparatus of claim 1 wherein the function generator comprises:

an electrical energy storage element;

a plurality of means connected to the storage element for successively augmenting or depleting the electrical energy stored in the storage element at predetermined rates corresponding to average slopes of segments of the predetermined curve of fuel quantity per injection;

a plurality of delay circuits, each delay circuit being associated with one of the plurality of means for augmenting or depleting the electrical energy stored in the storage element and connected to the pulse generator for actuating its associated energy augmenting or depleting means at a different predetermined delay time after said first pulse, each delay time corresponding to the start of the related segment of said predetermined curve, whereby the voltage across the energy storage element increases and decreases as a function of time following said first pulse in conformance with the predetermined curve of fuel quantity per injection to develop said analog reference voltage;

3. The injection control apparatus of claim 2 wherein each of the plurality of means for augmenting or depleting the electrical energy stored in the storage element comprises a currentgenerator .for permitting a flow of current between the energy storage element and a positive or a negative voltage supply, respectively, in response to an actuating signal from its associated delay circuit.

4. The injection control apparatus of claim 3 wherein each of the plurality of delay circuits comprises a monostable multivibrator, each of the monostable multivibrators having an unstable state of different predetermined time period and being triggered into its unstable state by the first triggering pulse, for actuating its associated electrical energy augmenting or depleting means at the termination of its unstable state.

5. The injection control apparatus of claim 4 wherein the plurality of current generators'and monostable multivibrators comprise:

a first monostable multivibrator having a first unstable time period approximately equal to the time between successive triggering pulses at maximum engine speed;

a first current generator actuated upon termination of the unstable period of the first monostable multivibrator for conducting current to the electrical energy storage element to augment the energy stored in the element at a first substantially constant rate;

a second monostable multivibrator having a second unstable time period approximately equal to the time between successive triggering pulses at the engine speed corresponding to maximum fuel demand per injection;

a second current generator actuated upon termination of the unstable period of the second monostable multivibrator for conducting current from the electrical energy storage element to deplete the energy stored in the element at a second substantially constant rate, greater than the first rate;

a third monostable multivibrator having a third unstable time period approximately equal to the time betweensuccessive triggering pulses at minimum engine speed; and

a third current generator actuated upon termination of the unstable period of the third monostable multivibrator for conducting current to the electrical energy storage element to augment the energy stored in the element at a third rate, greater than the difference between the first and second rates. whereby the voltage across the electrical energy storage element increases approximately linearly between the ends of the second and third time periods, then decreases approximately linearly between the ends of the second and third time periods, and finally increases again after the end of the third time period.

6. The injection control apparatus of claim 5 wherein the first and third current generators each comprise an electrical resistance element, connected at one terminal to a voltage source, and a transistor connected between the other terminal of the resistance element and the electrical energy storage means, the transistor being rendered conductive at the termination of the unstable time period of the associated monostable multivibrator for conducting current from the source through the resistance element to the electrical energy storage element, and

the second current generator comprises an electrical resistance element, connected at one terminal to ground, and a transistor connected between the other terminal of the resistance element and the electrical energy storage element, the transistor being rendered conductive at the end of the unstable time period of the second monostable multivibrator for conducting current from the electrical energy storage unit through the resistance element to ground.

7. The injection control apparatus of claim 1 further comprising:

a first switching element connected to the pulse generator and to the output of the function generator for returning the value of the analog reference voltage to zero in response to each pulse from the pulse generator.

8. The injection control apparatus of claim 7 wherein the means for developing the regulating voltage waveform comprises:

an electrical energy storage element;

A current generator for augmenting at a predetermined rate the electrical energy stored in the storage element in response to termination of the rectangular delay signal from the delay signal generator.

a second switching element sensitive to the difference between the analog reference voltage and the voltage across the second energy storage element for diverting the current flowing from the current generator away from the energy storage element when said voltage difference becomes approximately equal to zero; and

a third switching element responsive to actuation of the second switching element for applying the analog reference voltage to the energy storage element.

9. The injection control apparatus of claim 8 further comprising:

a fourth switching element in parallel with the electrical energy storage element for reducing the voltage across the storage element to zero in response to the termination of each fuel injection pulse from the fuel injection signal generator.

10. The injection control apparatus of claim further comprising:

an engine starter switch and a normally open timedelay switch connected between the pulse generator and the third monostable multivibrator and actuated by the engine starter switch for preventing triggering pulses from actuating the third monostable multivibrator except when the engine is being started.

11. The injection control apparatus of claim 4 wherein each monostable multivibrator comprises:

a voltage source;

a variable resistance having one terminal connected to one terminal of the voltage source;

a voltage divider connected across the voltage source and having a tap connection for supplying a predetermined voltage intermediate the voltages at the source terminals;

a programmable unijunction transistor having an anode connected to the other terminal of the variable resistance, a cathode connected to the other terminal of the voltage source, and a control electrode connected to the top of the voltage divider;

a capacitor connected in parallel with the anodecathode circuit of the programmable unijunction transistor; and

an input transistor having a base, a collector and an emitter, its collector-emitter circuit being connected in parallel with the capacitor and its base being connected to the pulse generator, the input transistor becoming conductive for the duration of each pulse from the pulse generator for discharging the capacitor and thereby rendering the unijunction transistor nonconductive, the capacitor subsequently charging through the variable resistance until its voltage reaches a value in relation to the intermediate voltage on the control electrode of the unijunction transistor sufficient to render the unijunction transistor conductive again, and the charging time for the capacitor being predetermined by adjustment of the variable resistance.

12. The injection control apparatus of claim 8 wherein the means for developing a regulating voltage waveform further comprises:

a unidirectional current control device having one terminal connected to the current generator and the other terminal connected to one terminal of the electrical energy storage element for providing a low resistance path for charging current from the current generator to the energy storage element and a resistive element connected in parallel with the unidirectional current control device for providing a high resistance path for discharging current from the energy storage element, the second switching element being connected to the junction between the current generator and the one terminal of the unidirectional current device for diverting the current flow from the current generator without simultaneously discharging the energy storage element.

13. The injection control apparatus of claim 12 wherein:

the second switching element comprises a programmable unijunction transistor having an anode connected to the junction between the current generator and the unidirectional current control device, a control electrode connected to the output of the function generator, and a cathode connected to the other terminal of the energy storage device, whereby the unijunction transistor becomes conductive for bypassing the charging current from the current generator around the energy storage device when the voltage on its anode rises to approximately the voltage at the output of the function generator.

14. The injection control apparatus of claim 13 wherein:

the second switching element further comprises a load resistor connected between the cathode of the programmable unijunction transistor and the other terminal of the energy storage device for developing a control voltage when the unijunction transistor is conducting;

the third switching element comprises a first transistor having its base connected to the load resistor for becoming conductive in response to the control voltage developed when the programmable unijunction transistor is conductive and a second transistor having its base connected to the collector of the first transistor for becoming nonconductive in response to conduction of the first transistor and its collector connected to the output of the function generator; and

the apparatus further comprises an emitter-follower having its input connected to the collector of the second transistor and its output connected to the one terminal of the electrical energy storage device for applying the output ofthe function generator to the energy storage device when the second transistor is nonconductive.

. EETAZEE @FFEQE QEETEFECATEE RRETION Patent No 358OO97L Dated April 2,

lnventorzx) Pierre M. Advenier It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, lines 20 2l: "onns'izantfl Column 1, lineQl: after mamlmzainin15 rlelete "constantm Column 1, line #62 after "efficiency" insert a close parenthesis Column 2, line l t: after "generator" insert a comm Column 2, line 3L: delete "et".,

Column 2, lines 5 4-55: delete "determined by the said".

Column 2, line 56, after "injection" insert Column 3 line 3: after "direction" change "of" to -to--.

Column 3, line 382 delete "being provided". I

Column 3, line #2: after "finally" insert an -'-a-.

Column 3, line 62: change "un'idirectly" to --indirectly-.

Column 5, line 2: before "pressure" insert an --a--.

Column 5, line 10: after "delaf delete as" and insert --signal--.

Column 5, line 11: before "first" insert -a---.

Column 6, line 63: change "01.2" to --GI.2-.

Column 6, line 6 change "(31.3" to "G143".

FORM PC4050 (10-69) USCOMM-DC 60376-1 59 fi U.S. GOVERNMENT PRI NTING OFFICE i959 0-366-334 Page; UNHEE STATES m'lENT oFmcE CERTIFICATE OF QDRRECTION Patent No. 3,800,799 bated p l 2, 197

Inventor( Pierre Mo Advenier It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 50: change ""cherfore" to -therefore-,

- Column 8, line 58: change "Roll to --P..,ll-. Column 9, line 1: change "is" to "13-". I

Column 9, line L6: change "VR" to "VH Colnmn 9, line 66: change "than" to "then- Column l0, line 6: delete "transistor". 9 Column 10, line 7: change "che" to "the- Column 11, line 62: change "T5" to --T.2--. Column 12, line 3 change "reistor" to resistorm Signed and sealed this 22nd day of October 1974.

(SEAL) Attest:

McCOY M. GIBSGN JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-1050(10-69) USCOMM'DC 60376-P69 b U.S. GOVERNMENT PRINTING OFFICE: 1969 O-366-J34. 

1. An electronic apparatus for controlling the injection periods of diesel engines having electromagnetic fuel injectors in accordance with a predetermined relation between injection period and engine speed under full load, the apparatus comprising: a pulse generator synchronized with engine rotation for providing a short triggering pulse corresponding to each successive injection period; a function generator connected to the pulse generator for developing an analog reference voltage in response to a first triggering pulse from the pulse generator, the value of the analog reference voltage varying as a function of time after the first triggering pulse so as to reproduce a predetermined curve of fuel quantity per injection versus time between injections under full load conditions at all engine operating speeds, the development of the analog reference voltage being terminated in response to a second triggering pulse next succeeding the first triggering pulse from the pulse generator; means for selecting a desired engine speed; a delay signal generator connected to the pulse generator and the speed selecting means for initiating a rectangular delay signal of variable duration in response to the first triggering pulse, the duration of the signal being controlled by the speed selection means as an inverse function of the selected speed; means connected to the pulse generator, the delay signal generator and the function generator for developing a regulating voltage waveform that is initiated in response to the termination of the rectangular delay signal, that rises from zero at a predetermined rate until it corresponds in value to the analog reference signal, and that follows the value of the analog reference signal until receipt of the second triggering pulse next succeeding the first pulse from the pulse generator; and a fuel injection signal generator connected to the pulse generator and to the means for developing the regulating voltage waveform for initiating in response to the second triggering pulse a rectangular fuel injection signal for actuating one of the fuel injectors, the duration of the fuel injection signal being determined by the value of the regulating voltage at the instant of the second triggering pulse, the second triggering pulse then serving as a first triggering pulse for initiating development of the analog reference voltage by the function generator for controlling the duration of the next succeeding fuel injection signal, whereby the amount of fuel injected during each fuel injection signal will increase to full load values if engine speed falls below the set speed and will decrease to zero if engine speed increases above the set speed.
 2. The injection control apparatus of claim 1 wherein the function generator comprises: an electrical energy storage element; a plurality of means connected to the storage element for successively augmenting or depleting the electrical energy stored in the storage element at predetermined rates corresponding to average slopes of segments of the predetermined curve of fuel quantity per injection; a plurality of delay circuits, each delay circuit being associated with one of the plurality of means for augmenting or depleting the electrical energy stored in the storage element and connected to the pulse generator for actuating its associated energy augmenting or depleting means at a different predetermined delay time after said first pulse, each delay time corresponding to the start of the related segment of said predetermined curve, whereby the voltage across the energy storage element increases and decreases as a function of time following said first pulse in conformance with the predetermined curve of fUel quantity per injection to develop said analog reference voltage.
 3. The injection control apparatus of claim 2 wherein each of the plurality of means for augmenting or depleting the electrical energy stored in the storage element comprises a current generator for permitting a flow of current between the energy storage element and a positive or a negative voltage supply, respectively, in response to an actuating signal from its associated delay circuit.
 4. The injection control apparatus of claim 3 wherein each of the plurality of delay circuits comprises a monostable multivibrator, each of the monostable multivibrators having an unstable state of different predetermined time period and being triggered into its unstable state by the first triggering pulse, for actuating its associated electrical energy augmenting or depleting means at the termination of its unstable state.
 5. The injection control apparatus of claim 4 wherein the plurality of current generators and monostable multivibrators comprise: a first monostable multivibrator having a first unstable time period approximately equal to the time between successive triggering pulses at maximum engine speed; a first current generator actuated upon termination of the unstable period of the first monostable multivibrator for conducting current to the electrical energy storage element to augment the energy stored in the element at a first substantially constant rate; a second monostable multivibrator having a second unstable time period approximately equal to the time between successive triggering pulses at the engine speed corresponding to maximum fuel demand per injection; a second current generator actuated upon termination of the unstable period of the second monostable multivibrator for conducting current from the electrical energy storage element to deplete the energy stored in the element at a second substantially constant rate, greater than the first rate; a third monostable multivibrator having a third unstable time period approximately equal to the time between successive triggering pulses at minimum engine speed; and a third current generator actuated upon termination of the unstable period of the third monostable multivibrator for conducting current to the electrical energy storage element to augment the energy stored in the element at a third rate, greater than the difference between the first and second rates, whereby the voltage across the electrical energy storage element increases approximately linearly between the ends of the second and third time periods, then decreases approximately linearly between the ends of the second and third time periods, and finally increases again after the end of the third time period.
 6. The injection control apparatus of claim 5 wherein the first and third current generators each comprise an electrical resistance element, connected at one terminal to a voltage source, and a transistor connected between the other terminal of the resistance element and the electrical energy storage means, the transistor being rendered conductive at the termination of the unstable time period of the associated monostable multivibrator for conducting current from the source through the resistance element to the electrical energy storage element, and the second current generator comprises an electrical resistance element, connected at one terminal to ground, and a transistor connected between the other terminal of the resistance element and the electrical energy storage element, the transistor being rendered conductive at the end of the unstable time period of the second monostable multivibrator for conducting current from the electrical energy storage unit through the resistance element to ground.
 7. The injection control apparatus of claim 1 further comprising: a first switching element connected to the pulse generator and to the output of the function generator for returning the value of the analog reference voltage to zero in responsE to each pulse from the pulse generator.
 8. The injection control apparatus of claim 7 wherein the means for developing the regulating voltage waveform comprises: an electrical energy storage element; A current generator for augmenting at a predetermined rate the electrical energy stored in the storage element in response to termination of the rectangular delay signal from the delay signal generator. a second switching element sensitive to the difference between the analog reference voltage and the voltage across the second energy storage element for diverting the current flowing from the current generator away from the energy storage element when said voltage difference becomes approximately equal to zero; and a third switching element responsive to actuation of the second switching element for applying the analog reference voltage to the energy storage element.
 9. The injection control apparatus of claim 8 further comprising: a fourth switching element in parallel with the electrical energy storage element for reducing the voltage across the storage element to zero in response to the termination of each fuel injection pulse from the fuel injection signal generator.
 10. The injection control apparatus of claim 5 further comprising: an engine starter switch and a normally open time-delay switch connected between the pulse generator and the third monostable multivibrator and actuated by the engine starter switch for preventing triggering pulses from actuating the third monostable multivibrator except when the engine is being started.
 11. The injection control apparatus of claim 4 wherein each monostable multivibrator comprises: a voltage source; a variable resistance having one terminal connected to one terminal of the voltage source; a voltage divider connected across the voltage source and having a tap connection for supplying a predetermined voltage intermediate the voltages at the source terminals; a programmable unijunction transistor having an anode connected to the other terminal of the variable resistance, a cathode connected to the other terminal of the voltage source, and a control electrode connected to the top of the voltage divider; a capacitor connected in parallel with the anode-cathode circuit of the programmable unijunction transistor; and an input transistor having a base, a collector and an emitter, its collector-emitter circuit being connected in parallel with the capacitor and its base being connected to the pulse generator, the input transistor becoming conductive for the duration of each pulse from the pulse generator for discharging the capacitor and thereby rendering the unijunction transistor nonconductive, the capacitor subsequently charging through the variable resistance until its voltage reaches a value in relation to the intermediate voltage on the control electrode of the unijunction transistor sufficient to render the unijunction transistor conductive again, and the charging time for the capacitor being predetermined by adjustment of the variable resistance.
 12. The injection control apparatus of claim 8 wherein the means for developing a regulating voltage waveform further comprises: a unidirectional current control device having one terminal connected to the current generator and the other terminal connected to one terminal of the electrical energy storage element for providing a low resistance path for charging current from the current generator to the energy storage element and a resistive element connected in parallel with the unidirectional current control device for providing a high resistance path for discharging current from the energy storage element, the second switching element being connected to the junction between the current generator and the one terminal of the unidirectional current device for diverting the current flow from the current generator without simultaneously discharging the energy storage element.
 13. The injection control apParatus of claim 12 wherein: the second switching element comprises a programmable unijunction transistor having an anode connected to the junction between the current generator and the unidirectional current control device, a control electrode connected to the output of the function generator, and a cathode connected to the other terminal of the energy storage device, whereby the unijunction transistor becomes conductive for bypassing the charging current from the current generator around the energy storage device when the voltage on its anode rises to approximately the voltage at the output of the function generator.
 14. The injection control apparatus of claim 13 wherein: the second switching element further comprises a load resistor connected between the cathode of the programmable unijunction transistor and the other terminal of the energy storage device for developing a control voltage when the unijunction transistor is conducting; the third switching element comprises a first transistor having its base connected to the load resistor for becoming conductive in response to the control voltage developed when the programmable unijunction transistor is conductive and a second transistor having its base connected to the collector of the first transistor for becoming nonconductive in response to conduction of the first transistor and its collector connected to the output of the function generator; and the apparatus further comprises an emitter-follower having its input connected to the collector of the second transistor and its output connected to the one terminal of the electrical energy storage device for applying the output of the function generator to the energy storage device when the second transistor is nonconductive. 